By Joachim Dagenborg and Tim Hepher
OSLO/PARIS (Reuters) - Norwegian investigators have provisionally ruled out pilot error in a helicopter crash that killed 11 oil workers and two crew, saying it was most likely caused by a technical fault.
An Airbus H225 Super Puma helicopter ferrying passengers from a Norwegian oil platform crashed in the North Sea on Friday, killing all 13 people on board.
"We are as certain as we can be that a technical error caused the accident. We don't think it was due to human misinterpretations," the director of Norway's Accident Investigation Board, Kaare Halvorsen, said on Tuesday.
Investigations remain at an early stage, however.
"The investigation will now solely be focused on potential root causes of a technical failure, such as design, production, and/or maintenance," Airbus Helicopters said in a statement.
Design and production are the responsibility of Airbus Helicopters, while maintenance is handled by the operator, CHC Helicopter.
Airbus, which had initially urged a halt to all Super Puma flights, said on Monday commercial operations could resume outside UK and Norway, since initial evidence did not suggest a link with earlier North Sea accidents.
Aviation sources said the European Aviation Safety Agency was nonetheless discussing with Airbus Group whether to issue a directive ordering worldwide checks on the Super Puma.
In total there are 179 H225 helicopters in service worldwide, including 40 operating in the North Sea.
The Norwegian investigation chief confirmed statements by CHC that the two pilots did not have time to send an emergency Mayday message before the crash.
The Super Puma is the workhorse of the oil industry, ferrying workers to and from offshore installations.
Friday's crash was the second-worst Super Puma accident after a 2009 crash off Scotland in which the rotors also detached, killing 16 people. Investigators cited a gearbox failure due to metal fatigue.
In 2012, Super Puma fleets were grounded after a pair of controlled ditchings that were later linked to gearbox cracks, prompting Airbus to carry out modifications.
Following the latest accident, Super Puma commercial flights were suspended in the UK and Norway, as well voluntary worldwide groundings by some operators.
Helicopter operators including CHC said they had been able to maintain service by using Sikorsky helicopters.
Oil firm Shell said on Monday it was suspending all flights in Norway with Canada-based CHC, but would continue using the firm in other countries.
(Additional reporting by Stine Jacobsen, writing by Gwladys Fouche, editing by Louise Heavens and David Evans)